Chrysotile asbestos clearly is cytotoxic and has been implicated as an etiologic factor in asbestosis and neoplasia in man and experimental animals. Very little is known concerning the early events of particle translocation and cell injury which lead to the characteristic diseases. To determine the initial impaction site and clearance pathways of inhaled fibers, rats were exposed to 4 mg/cubic m (respirable mass) of chrysotile asbestos for 1 hour. Animals were anesthetized immediately after each exposure, the tracheas were clamped, and the lungs perfused with Karnovsky's fixative through the right ventricle. Blocks of tissue were prepared for light, transmission and scanning electron microscopy. We have shown that inhaled asbestos impacts initially on alveolar duct bifurcations and that significant interactions take place between the asbestos and underlying alveolar duct epithelial cells. Early clearance through the alveolar epithelium could be a highly significant mechanism for introducing small asbestos fibrils into the pulmonary interstitium where interactions with macrophages and fibroblasts are known to occur during the pathogenesis of asbestos.